take over of proprietorship by son

what is your question

When business is transferred as going concern to another person is not treated as supply as per sec 7(1)(d) CGST ACT

my father is a composition dealer with stock around 10 lakhs.. he also earn comercial rent of rs 1lakh per year only..
gst act says any service provider cannot opt for composition scheme..
that is why he wants to transfer his business to his sons name..

the son is planning to get gst registration on 1st april 2018
what is the process??
do he have to pay gst on stock in hand or not?